The use of communication cables which include a plurality of optical fibers is rapidly expanding. An optical fiber cable may comprise a plurality of glass fibers each of which is protected by at least one layer of a coating material. The optical fibers may be assembled into units in which the fibers are held together by binder ribbons or tubes to provide a core. Another optical fiber cable core includes a ribbon-type optical fiber arrangement in which a plurality, such as twelve fibers, for example, are arrayed together side by side. A plurality of these ribbons may be stacked to obtain a high fiber count cable. The core is enclosed by a plastic core tube and a plastic jacket.
Whatever the structure of a cable, there must be provisions for splicing transmission media at an end of a given length of cable to corresponding transmission media at an adjacent end of another length of cable. In wire-like metallic conductor communication practice, it is conventional to use a splice closure, within which strength members of the cable ends may be anchored and all conductors spliced, wrapped and stored, and protected environmentally. During the splicing of metallic conductors, it is customary to sharply bend the conductors to provide access to other connections.
The physical nature of glass optical fibers prevents the use of splicing techniques which are used with metallic conductors within such a splice closure. Because of their small size and relative fragility, special considerations must be given to the handling of optical fibers in closures. Transmission capabilities may be impaired if an optical fiber is bent beyond an allowable bending radius, the point at which light no longer is totally contained in the core of the fiber. Furthermore, fibers are brittle and their expected lives will be reduced if bent more than the minimum bending radius. Generally, the radius at which the optical fiber can be bent without affecting orderly transmission is substantially greater than that radius at which the optical fiber will break. Whereas glass and silica, the materials used to make optical fibers, are stronger than steel in some respects, optical fibers normally do not possess this potential strength because of microscopic surface fractures, which are vulnerable to stress and spread and which cause the fiber to break easily.
It should be clear that optical fiber cable does not lend itself to the splicing practices of wire-like communication conductors. The individual glass fibers cannot merely be twisted, tied, wrapped and moved into a splice closure, as is the usual practice with wire-like metallic conductor cables. These small-diameter glass fibers cannot be crimped or bent at small angles, without breakage. Due to the fact that glass fibers have memory and tend to return to a straight line orientation, placement in a splice closure becomes somewhat difficult. Moreover, the interconnection of optical fibers is a precision operation which, in the past, has tended to discourage the performance of splicing operations within areas such as a manhole, a duct, or a pole-suspension elevation. And yet, to do otherwise becomes more expensive.
These problems are particularly acute in multifiber cables because individual optical fibers must be spliced in a manner which allows repairs and rearrangements to be made in the future. In addition, fiber slack normally must be provided adjacent to the splices. The need to store the slack further complicates the problem of providing a suitable optical fiber closure.
When splicing optical fibers by fusion or by mechanical means, it becomes necessary to provide enough slack fiber so that the fiber can be pulled out of the splice case for the preparation of fiber ends and the joining together. This requires at least about 0.5 meters of fiber from each cable to be stored inside of the splice closure once the splicing is completed and the closure is sealed. This slack forms what is commonly referred to as the fiber loop. For a multifiber cable, some method of storing the fiber loop, of protecting the splice and of keeping the fiber loops together in an orderly manner is required. The splices should be easily accessible to facilitate the rearrangement of the optical fibers and splices as well as repairs.
A fiber communications interconnection box, commonly known as a zone wiring box, is a strain relief and splice closure used to convert from a large cable containing a large quantity of individual optical fibers into the individual optical fiber communication paths provided by each optical fiber. The interconnection boxes may be used, for example, in a large business office which has many terminations for providing separate communication paths for various purposes. When terminating each optical fiber, a length of buffer fiber approximately one meter in length is exposed by stripping back the cable sheath in order to provide a termination of the cut fiber with a plug connector. After the plug connector is secured to the cut end of the optical fiber, the plug connector is inserted into a coupling on the inside of the interconnection box. When the plug connector is inserted into the coupling, a loop of buffered fiber is formed, which is referred to herein as a buffer loop. Each fiber has a buffer loop and the management of these loops inside of a typical interconnection box is difficult.
Prior art interconnection boxes contain spools around which the buffer loops are wrapped in a circular fashion. One problem with these systems is that, when the loops are wrapped around the spools, the length of the fiber forming the loop generally does not match an integral number of revolutions around the spool. As a result, unraveling may occur due to loosening. This problem is exacerbated when a large number of buffer loops are managed within a small area, which normally is the case. Furthermore, in most cases the spools must have a radius equal to or greater than approximately 0.75 inches to prevent the fibers from being bent into too small of a radius. Another problem with these systems is that the buffer loops generally are wrapped snugly about the spools. Since each spool typically holds several fiber loops, unwrapping the loops from the spools when repairs need to be made is difficult.
Below et al. discloses an optical fiber interconnection system which is a patch panel for interfacing optical fibers with optoelectronic equipment which converts the optical information into electrical information. The patch panel includes a tray means for supporting a coiled bundle of fibers, and clips mounted on the tray means for retaining the coiled portions of the fibers within the patch panel. Cable supports extending from the front surface of the patch panel limit the bending radii of the coiled fibers. One of the disadvantages of the system disclosed in Below et al. is that the excess fiber retained within the patch panel generally will not have lengths equal to an integer number of coils around the tray means, which may result in excess fiber that is not retained by the clips and thus, poor management of the fiber loops within the patch panel.
Accordingly, a need exists for an optical fiber loop management system which is capable of handling a large number of buffer loops and which overcomes the deficiencies of prior art optical fiber loop management systems.